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The small difference in wavelength between an argon laser (514 nm) and a frequency-doubled Nd:YAG laser (532 nm), together with the advantage of the solid-state technology, makes the Nd:YAG laser likely to play a major role in retinal photocoagulation in the near future. For technical reasons all frequency-doubled Nd:YAG lasers work in a quasi-continuous mode, emitting a burst of highly repetitive short laser pulses during the exposure time desired. We investigated the side effects due to high peak irradiances of those short laser pulse trains (Crystal Focus Nd:YAG laser, Emerald; pulse duration 1-10 microseconds, repetition rate 13 KHz) in rabbits in comparison with a standard argon laser system (Zeiss, Visulas, Argon II). The energy necessary for blanching the retina was similar in both cases. As opposed to the argon laser system, subretinal bubbles were regularly visible ophthalmoscopically with the Nd:YAG system, when average powers as high as 200 mW were used. The ED50 power for bubble formation is about 2-3 times above the ED50 power for blanching. Thermal calculations show that this bubble formation effect is likely to be related to the peak power of the short pulses. The hemorrhage threshold is similar in both systems. However, light microscopically there is no difference between the two laser systems. Panretinal photocoagulation (300-500 microns, 100-200 ms) in patients with proliferative diabetic retinopathy produced such bubbles about once per 1000 lesions.
Of 21 retinal detachments with a macular hole, 18 (86%) were cured by cerclage, combined with drainage of the subretinal fluid and light (laser) coagulation of the macula. By means of this simple procedure, recommended by Meyer-Schwickerath in 1961, many surgical difficulties and possible complications, especially posterior pole hemorrhages, can be avoided and relatively good function of the central retina can be achieved. Even highly myopic eyes with moderate staphyloma can be treated successfully by this technique.
PURPOSE: Comparison of the effectiveness and safety of cyclocryocoagulation and transscleral contact cyclophotocoagulation with diode laser (TSCPC) in children. PATIENTS AND METHOD: Sixty nine eyes of 60 children at the age from 4 months to 16 years were examined. Majority of patients was aphakic after congenital, traumatic and complicated cataract extraction. Aniridia, Sturge-Weber disease and ROP complications were observed. In 40 eyes cyclocryotherapy (I group), in 29 eyes TSCPC (II group) were performed. Intraocular pressure (IOP) was assessed in the early and late postoperative period. The number of procedures per one eye, IOP, visual acuity, and complications after cyclodestructive procedures were estimated. Follow-up ranged from 3 months to 4 years, mean 23 months. RESULTS: Transscleral cyclocryocoagulations were performed once to 4 times in one eye with intervals from 1 month to 1 year, mean 1.3 procedures per eye. TSCPC was performed once in 29 eyes and twice in 4 cases, it was 1.14 procedures per eye. Before treatment IOP ranged from 21.3 to 50.6 mmHg, mean 29.18 mmHg in the I group and 24.4-54 mmHg mean 34.85 mmHg in the II group and in the early postoperative period were 10-25 mmHg, mean 17.7 and 2-26 mmHg, mean 14.65 mmHg relatively. Decreasing of IOP was observed in 39% of eyes after cryotherapy and 57.9% after TSCPC, p = 0.0003. In the long-term follow-up in IOP below 22 mmHg after cyclocryotherapy in 60% of eyes and after TSCPC in 79% was observed. Visual acuity ranged from no light perception to 0.5, mean 0.04. No changes of vision after cyclocryocoagulation were noted. After TSCPC transient visual function decreased from 0.2 to 0.04 in 1 eye but recovered after 2 weeks. After cyclocryotherapy only conjunctival oedema was observed in majority of cases. In the early postoperative period after TSCPC uveitis occured in 3 eyes (10.35%), transient hypotony in 2 eyes, hyphaema in one eye. CONCLUSION: Diode cyclophtocoagulation decreases IOP more effective than cyclocryocoagulation in children but complications after TSCPC are more severe than after cyclocryotherapy.
The complete amino acid sequence of the light chain of human blood coagulation factor X has been determined by automated Edman degradation of peptides isolated from chemical and enzymatic digests of the carboxymethylated light chain. The protein consists of 139 amino acid residues, which include 11 residues of gamma-carboxyglutamic acid. The first 100 residues of the human factor X light chain exhibit approximately 80% homology when compared to the amino-terminal sequence of bovine factor X light chain. This homology decreases to approximately 50% in the remaining 39 residues of the carboxyl-terminal region of the protein. Proton nuclear magnetic resonance spectroscopy and mass spectrometry analyses of isolated residue 63 identified this residue as L-erythro-beta-hydroxyaspartic acid, a hitherto unrecognized amino acid in proteins. Evidence is also presented for the presence of this residue in the corresponding regions of the light chains of bovine factor X and bovine protein C. The biological function of beta-hydroxyaspartic acid in these proteins is unknown.
Free Running Neodymium-Yttrium Aluminum Garnet (FR Nd-YAG) laser coagulation of the macula was performed in seven human eyes. Follow-up varied from 1 to 15 days. Damage to the outer retinal layers was apparent immediately after exposure whilst that in the inner retinal layers developed subsequently. The choriocapillaris and major choroidal vessels were occluded. Visual acuity changed in an unpredictable way.
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The clinical findings in six patients with juvenile haemorrhagic macular choroidopathy are described. There was no evidence of infection with Histoplasma capsulatum. The history, clinical features and course of the disease suggested that at least in some cases intravascular coagulation in the central choriocapillaris may form the choroidopathy inducing the disciform detachment of the macula. Oral corticosteroids could not prevent progression of the lesion which had a poor visual outcome. In one patient, good therapeutic response was achieved with acetylsalicylic acid, which may be useful together with lasercoagulation in the early treatment of this syndrome.
Protein C activation by thrombin is significantly accelerated by the endothelial cell surface protein thrombomodulin, Factor Va, or its light chain. In this study we have compared the activation of protein C in the presence of either cofactor and examined the possibility that thrombomodulin and Factor Va-light chain act together to regulate protein C activation by thrombin. At all concentrations of protein C used, thrombomodulin was 20 times more efficient than Factor Va-light chain in accelerating protein C activation by thrombin. Protein C treated with chymotrypsin to remove the amino-terminal 41 amino acids that contain the gamma-carboxyglutamyl residues was activated by the thrombin-thrombomodulin complex at an identical rate to native protein C, whereas the modified protein C was activated by Factor Va-light chain and thrombin at only 5% of the rate obtained by using native protein C. Increasing concentrations of Factor Va-light chain, greater than or equal to 30 nM, inhibited thrombin-thrombomodulin catalyzed protein C activation with complete inhibition observed at 90 nM Factor Va-light chain. On the other hand, increasing thrombomodulin concentrations did not inhibit protein C activation by Factor Va-light chain and thrombin. These reactions in solution mimic, in part, those obtained on endothelial cells where protein C lacking the gamma-carboxyglutamyl domain is activated poorly and Factor Va-light chain at concentrations greater than 50 nM inhibited the activation of native protein C. The results of this study suggest that thrombomodulin and Factor Va-light chain may act in concert to regulate protein C activation by thrombin.
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